Reproducibility and Sensitivity of the 6-Minute Stepper Test in Patients with COPD

The aims of this study were to test the reproducibility of the 6-minute stepper test (6MST), and evaluate its accuracy in detecting improved functional capacity after pulmonary rehabilitation (PR) in patients with chronic obstructive pulmonary disease (COPD). Thirty-five COPD outpatients performed two 6MSTs in the same session, before (6MST(1) and 6MST(2)) and after (6MST(3) and 6MST(4)) PR. The performance, perceived exertion, heart rate and arterial oxygen saturation were measured during each 6MST. The performance was higher during the second 6MST of the same session (before PR: 514 strokes during the 6MST(2) > 471 strokes during the 6MST1, and after PR: 559 strokes during the 6MST(4) > 508 strokes during the 6MST(3); p = 0.04). After PR, 6MST performance was higher than before PR (6MST(3) > 6MST(1) and 6MST(4) > 6MST(2); P < 0.01). The bias (the difference in the number of strokes) between the two 6MSTs from the same session (before PR: 6MST(2)-6MST(1) = 42 strokes vs after PR: 6MST(4)-6MST(3) = 52 strokes) was not different (P = 0.34). However, both bias were greater than 0 (P < 0.001). The mean performances for the two 6MSTs of the same session (before PR: 6MST(1) and 6MST(2) and after PR: 6MST(3) and 6MST(4)) were correlated with the bias between these performances (P< 0.01; r = 0.32). The perceived exertions were lower after PR (P < 0.02). The systematic improvement of performance (8-10%) during the second 6MST of the each session may be explained from the warming of hydraulic jacks of the stepper and/or learning effect. On the other hand, the 6MST seems sufficiently sensitive to detect functional capacity improvements after PR in patients with COPD.